This application is related to and claims priority from Japanese Patent Applications No. Hei. 11-354812 filed on Dec. 14, 1999 and No. 2000-337839 filed on Nov. 6, 2000, the contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a pair of electrodes for detecting acidity or basicity of oil, which undergo a change in a potential difference in accordance with the acidity or basicity in oil. More particularly, the present invention relates to a reference electrode and a sensitive electrode constructing the pair of electrodes.
2. Description of the Related Art
Various kinds of oils such as fuel oil, working oil, quenching oil and lubricating oil have industrially been used. However, they are known to show a gradual increase in their acidity due to oxidation by air, accumulation of a combustion product or the like during storage or use and eventually undergo corrosion or an undesirable deterioration of their initial performances. It is therefore a matter of great importance in the maintenance of oil to detect its deterioration quickly and accurately.
For detecting such a deterioration of oil, for example, in U.S. Pat. No. 5,146,169, JP-A-6-201649 or JP-A-62-25250, a pair of electrodes are constructed by a sensitive electrode in which a potential difference varies in response to the acidity or basicity of the oil, and a reference electrode which is different from the sensitive electrode in an inclination degree representing a potential change.
Further, in a pair of electrodes as described in JP-A-62-25250, Pb (lead) is employed as a reference electrode for a pair of electrodes. Because Pb is however a substance hazardous to the environment, the use of Pb as a reference electrode is not desired.
On the other hand, as a sensitive electrode to be used in combination with a reference electrode, SUS (stainless) is conventionally known. In this case, an electrode portion is formed into a plate like, and its size inevitably becomes large, thereby deteriorating arrangement properties. In order to overcome such a problem, a size reduction of the electrode portion by using a semiconductor fabricating technique such as screen printing, deposition or sputtering is considered, but metals such as SUS are not suited for the fabrication technique.
In view of the foregoing problems, it is an object of the present invention to provide a pair of electrodes for detecting acidity or basicity of oil, which are made of a novel electrode material not hazardous to the environment but suitable for use in a semiconductor fabrication technique, and to provide a reference electrode and a sensitive electrode which can suitably used for the pair of electrodes.
According to the present invention, in a pair of electrodes where a potential difference is changed in accordance with acidity or basicity of oil, a reference electrode is made of cobalt or a cobalt alloy, and a sensitive electrode is made of tungsten or a tungsten alloy. The sensitive electrode is used in combination with the reference electrode. The cobalt or the cobalt alloy and the tungsten or the tungsten alloy are not substances hazardous to the environment, and it is possible to perform the manufacture of the electrodes by screen printing, deposition or sputtering. Accordingly, it is possible to provide a pair of electrodes for detecting the acidity or the basicity of the oil which use a novel electrode material not hazardous to the environment and at the same time, suited for use in a semiconductor fabrication technique.
Alternatively, the sensitive electrode combined with the reference electrode is made of titanium or a titanium alloy. In this case, the sensitive electrode has an oxide film on the surface thereof, and a thickness of the oxide film is in a range of 7-80 nm. Therefore, sensitive performance of the sensitive electrode can be improved. Accordingly, the same effect described above can be obtained.